The proposed research will evaluate the mechanisms by which hormones regulate the growth of kidney epithelial cells, and the alterations which occur upon malignant transformation. The MDCK cell line is particuarly advantageous as compared with other renal cell lines, for studies concerning hormonal regulation of growth as Medium K-1, a hormone supplemented, serum-free medium, has been developed which permits MDCK cells to grow in the absence of fetal calf serum (11). Following the methodologies developed in the laboratory of Dr. Gordon Sato (10), five supplements were identified (insulin, transferrin, T3, hydrocortisone and PGE1) which permitted MDCK cells to grow over a long term, and at an equivalent rate in serum-free and serum-supplemented medium (11). Medium K-1 has also been used to grow primary cultures of baby mouse kidney epithelial cells. Medium K-1 will be used for the following studies: (1) The possibility that PGE1 stimulates growth by increasing intracellular cAMP in MDCK cells will be examined. Available PGE1 independent variants of MDCK cells (variants which lack PGE1 requirement for long term growth in serum-free medium) will be utilized. 2) The possibility that malignant transformation is accompanied by changes in requirements of hormones for growth will be evaluated, utilizing available tumorigenic transformants of MDCK cells. (3) Growth regulation by hormones will also be examined in primary cultures of kidney epithelial cells. Medium K-1 was utilized to select epithelial cells from primary kidney cultures, whose growth responses to hormones resemble those of MDCK cells. In order to selectively grow different types of epithelial cells in primary kidney cultures, additional hormone-supplemented, serum-free media will be developed for kidney epithelial cell line which do not grow in Medium K-1.